The present invention relates to photonic chips and, more specifically, to structures including waveguide bends, methods of fabricating a structure that includes waveguide bends, and systems that integrate optical components containing different materials.
Photonic chips are capable of being used in many applications and many systems including, but not limited to, data communication systems and data computation systems. A photonic chip integrates optical components, such as waveguides, and electronic components, such as field-effect transistors, into a unified platform. Layout area, cost, and operational overhead, among other factors, may be reduced by integrating both types of components on a single photonic chip.
On-chip communication and sensing may rely on transferring optical signals through waveguides on the photonic chip to other optical components. Optical signals propagate as electromagnetic waves within waveguides using a number of different modes characterized by different properties. The transverse magnetic (TM) mode is dependent upon transverse magnetic waves in which the magnetic field vector is oriented perpendicular to the direction of propagation. The transverse electric (TE) mode is dependent upon transverse electric waves in which the electric field vector is oriented perpendicular to the direction of propagation.
Straight waveguides and waveguide bends, as well as other optical components, may have cores that are fabricated from silicon nitride or single-crystal silicon. For transverse magnetic mode, a waveguide or waveguide bend with a silicon nitride core may have a considerably lower effective index and a significantly weaker field confinement than a waveguide with a single-crystal silicon core. The weak confinement in a silicon nitride core is larger for transverse magnetic mode than for transverse electric mode. As a result, a portion of the mode field may be pulled outside of the silicon nitride core as optical signals propagate through a waveguide bend, which may lead to a higher bending loss in comparison with a waveguide bend of equal bending radius with a single-crystal silicon core. To compensate for the higher bending loss, a waveguide bend with a silicon nitride core may be provided with a larger radius of curvature than a waveguide bend with a single-crystal silicon core, which increases the footprint of waveguide bends with a silicon nitride core. Straight waveguides containing single-crystal silicon have also been observed to have large footprints or to experience significant propagation losses.
Improved structures including waveguide bends, methods of fabricating a structure that includes waveguide bends, and systems that integrate optical components containing different materials are needed.